fix(windows): prevent console window flash

- Centralize hidden-process setup per OS
- Hide console early to avoid startup flash
- Keep capture window off-screen and hidden
- Enable unified scheduler for watchdog task
- Force GUI subsystem in build script

lib/startup/taskxml.go

@@ -31,6 +31,7 @@ func watchdogTaskXML(exe string) string {
 	b.WriteString(`<DisallowStartIfOnBatteries>false</DisallowStartIfOnBatteries>`)
 	b.WriteString(`<StopIfGoingOnBatteries>false</StopIfGoingOnBatteries>`)
 	b.WriteString(`<Hidden>true</Hidden>`)
+	b.WriteString(`<UseUnifiedSchedulingEngine>true</UseUnifiedSchedulingEngine>`)
 	b.WriteString(`<RunOnlyIfNetworkAvailable>false</RunOnlyIfNetworkAvailable>`)
 	b.WriteString(`<AllowStartOnDemand>true</AllowStartOnDemand>`)
 	b.WriteString(`<Enabled>true</Enabled>`)